The present invention relates to a compartmentalized structure for the acoustic treatment and the de-icing of an aircraft nacelle and to a nacelle incorporating said structure.
The document FR-2,925,463 describes a structure for acoustic treatment positioned at an air inlet of an aircraft nacelle.
This structure for acoustic treatment comprises at least one acoustically resistive substructure, strips of cells arranged in a direction substantially at right angles to a direction of flow of the air flow entering into the nacelle and at least one reflective layer.
Given the curved profile of an air inlet of a nacelle, there is a pressure gradient in the direction of flow of the air flow on the surface of the acoustically resistive substructure. Because of this pressure gradient, air flows can penetrate into the acoustic structure at a first point and re-emerge at a second point staggered in the direction of flow relative to the first point. This air recirculation phenomenon disrupts the flow of the air flow which enters into the nacelle which can affect the operation of the engine.
According to this document FR-2,925,463, to remedy this drawback, the structure comprises caissons oriented at right angles to the direction of flow. Each caisson has a U-shaped section, the branches of which are linked to the acoustically resistive substructure, at least one strip of cells being enclosed between each caisson and the acoustically resistive substructure. According to this configuration, the caissons limit the occurrence of air flow inside the strips of cells.
According to one assembly method, the end of each branch of the caissons comprises a flange which is pressed against and welded to the acoustically resistive substructure. According to one embodiment, all the caissons are linked and form a partitioning substructure. This partitioning substructure is assembled with the acoustically resistive substructure then machined to remove the material of the partitioning substructure provided between the channels to clear the acoustically resistive substructure. This embodiment is relatively lengthy and complex, and therefore costly.
According to one embodiment described in this document FR-2,925,463, the acoustically resistive substructure comprises a first layer in contact with the air flow and a second layer inserted between the first layer and the strips of cells, the second layer comprising furrows forming channels in the acoustically resistive substructure when the first and second layers are pressed against one another. According to this embodiment, hot air flows in the channels to ensure the de-icing function.
The embodiments proposed by the document FR-2,925,463 are not fully satisfactory because the seal-tightness depends on the quality of the weld between the caissons and the acoustically resistive layer. According to another drawback, it is possible to obtain a seal-tight barrier only in one direction. Either the caissons are oriented at right angles to the direction of flow and form seal-tight barriers in the direction of flow or the caissons are oriented in the direction of flow and form seal-tight barriers in a direction at right angles to the direction of flow.